Method for extrusion molding of a self-locked nut

ABSTRACT

A method for extrusion molding of a self-locked nut employs molds to perform the following steps in a nut forming machine. The steps comprise: slug cutting off step for preparing a slug; trimming step for trimming the configuration of the slug to become predetermined size; flange pre-formation step for forming a flange prototype at one end face; flange adjusting and tooth portion forming steps for further adjusting the flange prototype of slug to be predetermined length and on the periphery of flange to form the straight row of tooth portion axially; punching step for forming a through hole axially on the slug after above steps and forming threads inside the through hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a forming method for an extruding nut, particularly to a cold forging method of a self-locked nut to produce a self-locked nut in high speed with no material loss.

2. Description of Related Art

Generally, the self-locked nut is known in the art. It is used to insert in a metal plate and provides with an anchor portion for the thread connection of a screw, so a part can be fixed on the metal plate through the screw. A kind of known self-locked nut, as shown in FIGS. 13 and 14, mainly includes a nut body 101′ and an anchor flange 102′ wherein there is a through inner thread hole 103′ for the connection of a screw (not shown) at the inside of nut body 101′ and anchor flange 102′. Furthermore, the top end face 104′ of nut body 101′ is formed as a shoulder and a straight row of tooth portion 105′ is formed along the outer peripheral surface of flange 102′. As shown in FIG. 14, this kind of nut is fixed on a metal plate 106′. At first, a hole on the metal plate 106′ is made to its diameter that is equivalent with that of neck portion of tooth portion 105′ on the flange 102′. Thus, when the portion of the flange 102′ is pressed through the hole of metal plate the metal plate 106′ can be clamped between the shoulder portion of top end face 104′ and the forced deformation of flange 102′, so the nut can not slide axially out of hole and the arbitrary rotation of nut body 101′ inside the hole of metal plate 106′ can be stopped by the friction force between straight row tooth portion 105′ and hole of metal plate.

So far, this kind of self-locked nut is manufactured by using a hexagonal automatic turret lathe and produce one by one. Imaginably, it requires slow material cutting steps during production. The yield is low, merely seven pieces in amount per minute. In order to enhance the production it will surely need to purchase a lot of expensive automatic turret lathes to produce a certain amount. In addition, since the cut material is waste it also increases the material cost. Thus, using automatic turret lathe to produce self-locked nut has the problems of low production speed, high cost for the production equipment and high material cost and results in high price of nut.

SUMMARY OF THE INVENTION

In view of conventional self-locked nut manufacturing method, however it has the disadvantages of impossibly further increasing the production speed by a lathe and lowering the production cost. The main object of this invention is to provide a continuous extrusion molding method to produce self-locked nut with cold forging to the effect that it can increase the production speed and decrease the cut material waste, thus lower the production cost.

According to the method of this invention, the manufacturing steps of steps comprise: cutting a rod material into a piece of slug and feeding into a mold; pressing the slug within plural molds to experience multiple pressing steps to trim the rough surface of the slug into smooth surface with predetermined size as semi-product: pressing the semi-product to form a flange prototype in a mold at one end face of semi-product: pressing the semi-product having flange prototype in a mold and completing the sharp of the flange and at the same time forming straight row tooth portion at the outer periphery of flange; piercing the slug axially to form an axial though hole; forming thread by tapping at the inner wall of through hole.

According to the method of this invention, it can employ a generally known nut forming machine to perform each extrusion step of the invention. The production speed is high and achieves more than fifty pieces per minute and the material loss (i.e. the cut material) is one fifth of known automatic turret lathe. Thus, it is another object of this invention that the equipment cost of installation is low as well as the production speed can be increased and the stock cost can be lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of manufacturing steps for manufacturing self-locked nut with extrusion forge means according to this invention.

FIG. 2 is a schematic view of a cut slug from a coil of metal material.

FIGS. 3, 4 and 5 are schematic views of showing three steps for the slug undergoing configuration trimming within molds.

FIG. 6 is a schematic view of pre-forming flange prototype of slug formed in FIG. 5 within the mode.

FIGS. 7 a-b are schematic views of further adjusting flange and forming tooth portion of slug having flange prototype shown in FIG. 6.

FIGS. 8 a-b are schematic views of making a through hole of slug shown in FIG. 7 by pressing.

FIG. 9 is a schematic view of forming inner thread by tapping within the through hole shown in FIG. 8.

FIG. 10 is a schematic view of a mold used for trimming slug shown in FIGS. 3, 4 and 5.

FIG. 11 is a schematic view of a mold for forming slug having flange prototype shown in FIG. 6.

FIG. 12 is a schematic view of a mold for forming slug having predetermined flange and tooth portion shown in FIG. 7.

FIG. 13 is a schematic perspective view of a known self-locked nut.

FIG. 14 is a schematic cross view showing a self-locked nut of FIG. 13 pressed into a hole of a plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For further understanding of extrusion molding method, the objects and advantages of self-locked nut provided by this invention are illustrated as following in accordance with accompanying figures.

At first, referring to FIG. 1, the extrusion molding step for self-locked nut of this invention comprised: (1) slug cutting step, making a slug from a coil of metal rod by cutting (2) trimming step, extruding the slug and forming into predetermined size with smooth surface in appearance; (3) flange pre-forming step, forming a nut body at the trimmed slug and pre-forming a flange prototype at one end face of the nut body; (4) flange adjusting and tooth portion forming step, extruding the per-formed flange to predetermined size, at the same time, forming a series of straight tooth portion axially along the periphery of the flange; (5) punching a through hole step, forming a through hole axially along slug by pressing; and (6) tapping step, forming thread on the inner wall surface of the through hole. The implementation of above steps will be illustrated according to the following embodiment.

Regarding the implementation of above steps for each step of this invention, it is performed by using known nut forming machine, i.e. a slug will pass a series of molds sequentially to accomplish.

(1) Slug Cutting Off Step

According to a conventional cutting device installed on the known nut forming machine, a constant length of slug 1 is cut off from a coil of metal rod as shown in FIG. 2.

(2) Trimming Step

Referring to FIG. 10, three trimming forming molds 2 are installed sequentially at the first, second, third work stations of nut forming machine. Each mold 2 comprises: a nut cavity 2 a with size matching an upper punch 11 a (referring to FIG. 3) and slug 1 being fed into the cavity through nut forming machine; a lower cavity 2 b, matched with a lower punch 11 b (referring FIG. 3) the upper punch 11 a and lower punch 11 b are activated by nut forming machine and can move relatively inside the mold 2 installed at the first pressing work station, and then making slug 1 fed into mold 2 been pressed to become the first slug 1 a. As shown in FIG. 3, the lower punch 11 b presses a cavity 1′a at the lower end face of the first slug 1 a. The purpose of which is to make the material of slug 1 to flow plastically outward to conform with the configuration of inner wall of cavity 2 a of mold 2 and makes the slug have smooth surface. At the same time, the cavity 1′a can pre-form the thread hole which will be explained late.

Then, by the use of the original material feed-out and feed-in devices of nut forming machine the first slug la is clipped and rotated by 180 degrees, then fed into the second mold 2 fixed at the second pressing work station. By the upper punch 11′a and lower punch 11′b as shown in FIG. 4, further press the first slug 1 a into the second slug 1 b. Herein, the bottom 1′b shape of the second slug 1 b formed at the second pressing work station has been extruded to conform with the bottom shape of cavity 2 a of mold 2. At the same time, the cavity 1′a of first slug 1 a is further formed as deeper cavity 1″a.

Then, by the use of the original material feed-out and feed-in devices of nut forming machine the second slug 1 b is rotated by 180 degrees, then fed into the third mold 2 at the third pressing work station. And by the upper punch 11′a and lower punch 11′b as shown in FIG. 5, further press second slug 1 b into third slug 1 c. At this time, the bottom 1′c shape of the third slug 1 c also conforms with the bottom shape of cavity 2 a of mold 2. Thus, the size of whole appearance of formed third slug 1 c, after such three times pressing, has predetermined value and has smooth appearance with inward cavity 1″a, 1″c at upper and lower end face respectively.

So far, the initial slug 1 after undergoing pressing forging at the first, second, third work stations has been completed the trimming step of slug 1. The trimmed semi-product of slug 1 c will be transferred into next flange pre-forming station.

(3) Flange Pre-Forming Step

Referring to FIG. 11, the mold 3 used in flange pre-forming step has a nut cavity 3 a and lower cavity 3 b inside the mold, being substantially similar to the trimming mold 2. It is different that its round corner R2 is bigger than the round corner R1 of mold 2. Mold 3 is fixed at the fourth pressing work station of nut forming machine, and operated by nut forming machine with the upper punch 12 a matching nut cavity 3 a and the lower punch 12 b matched with cavity 3 b those move relatively inside the mold3.

The semi-product of extruded slug 1 c through the trimming step is then rotated by 180 degrees by the stock feed-out and feed-in devices of nut forming machine and fed into the mold 3 fixed at the fourth pressing work station, as shown in FIG. 6, after pressing a slug 1 d with flange 1′d at front end face of slug 1 c is shaped by the contour of R2. Obviously, the prototype of flange 1′d is formed by forcing the material of slug to flow plastically with the top end shape of lower punch 12 b and extrusion-of upper punch 12 a. At the same time, the cavities of upper and lower end faces of slug id is further deepened by lower, upper punches.

(4) Flange Adjusting and Tooth Portion Forming Step

Flange adjusting and tooth portion forming steps are implemented by the adjusting mold 4 as shown in FIG. 12. The difference between mold 4 and two pressing molds above-mentioned is that the axial straight row tooth portion 401 is formed at the inner wall of lower cavity 4 b. Mold 4 is fixed at the fifth pressing work station of nut forming machine, and the upper punch 13 a and the lower punch 13 b of nut forming machine are activated in nut forming machine and moved inside the mold 4.

Slug 1 d formed at fourth pressing work station is transferred into mold 4 by the stock feed-out and feed-in devices of nut forming machine, through the pressing of upper punch 13 a and lower punch 13 b , the prototype of flange 1′d of slug 1 d is further prolonged to predetermined length by flowing plastically inside the lower cavity 4 b. At the same time, through the tooth portion 401 of lower cavity 4 b a straight row tooth portion 1″e is formed at the flange 1′d. Then a slug 1 e is formed as in FIG. 7 a.

While the axial straight row tooth portion 401 of mold 4 is adjusted to proper length during the flange adjusting and tooth portion forming step, the prototype of flange 1′d of slug 1 d is flowed plastically inside the lower cavity 4 b by pressing with upper punch 13 a and lower punch 13 b, and the top end periphery of flange 1′d is formed directly a trumpet shape as the anchor protrusion 102′. Then the slug 1′e is formed as in FIG. 7 b.

According to the semi-product of made by the mentioned above steps, compared with semi-product of slug id shown in FIG. 6, the depths of cavities of upper and lower end faces of slug 1 e or 1′e have been deepened.

(5) Punching a through Hole Step

Slug 1 e or 1′e formed at fifth pressing work station is rotated by 180 degrees by the stock feed-out and feed-in devices of nut forming machine to the effect that the flange is in the upper position and transferred into the mold(not shown), fixed at sixth pressing work station. Then, the cavity of slug 1 e or 1′e is pierced by upper punch 14 a as shown in FIG. 8 a or 8 b to form a through hole 101. Thus, a semi-product of slug 1 f is formed and collected from the stock feed out of nut forming machine.

Through the above steps of this invention, so far the extrusion-molded appearance and configuration of a self-locked nut has accomplished. Furthermore, although the steps are illustrated respectively, they are implemented sequentially at the same time in a nut forming machine.

(6) Tapping Step

Then, the collected formed semi-product of slug 1 f, as shown in FIG. 9, is taped inner thread 103 within the through hole 101 by the known tapping machine and finally accomplishes an extrusion-molded self-locked nut 1 g product.

Furthermore, if a self-locked nut with a larger tensile for it is required, the top end periphery of flange 1′d is increased to form a trumpet shape as anchor protrusion 102′, thus increases the capability of being uneasily pulled out after nut 1 g pressed into the opening of a metal plate. For example, the flange adjusting and tooth portion forming step mentioned above, if modifying the axial straight row tooth portion 401 of mold 4 to proper length trumpet shape anchor protrusion 102′, as shown in FIG. 7 b, can be formed directly; or after forming slug 1 g as shown in FIG. 9, by cutting off part of top end periphery of tooth portion 1″e a large trumpet shape is formed as an anchor protrusion 102′ in the tapping step.

In sum, by using extrusion molding method of self-locked nut of this invention the cost of installation equipment can be reduced and the production speed of self-locked nuts can be promoted, and the waste material is decreased and the material cost is low. List of numeral symbols of main parts 1, 1d, 1e, 1′e, 1f, 101′ slug 1a first slug 1′a, 1′′a, 1′′′a, 1′′c cavity 1b second slug 1c third slug 1′b, 1′c bottom 1″e, 401 tooth portion 1′d flange 2, 3, 4 mold 2b, 3b, 4b lower cavity 2a, 3a nut cavity 11a, 11′a, 11″a, 12a, 13a, 14a upper punch 11b, 11′b, 11′′b, 12b, 13b lower punch 101 through hole 102′ anchor protrusion 103 inner thread R2, R1 round corner 

1. A method for extrusion molding of a self-locked nut, which uses molds to perform the following steps in a nut forming machine: (1) a step of preparing a cylindrical slug with two end face; (2) a step of trimming the configuration of the slug to predetermined size; (3) a step of flange pre-forming a flange prototype at one end face of trimmed slug; (4) a step of flange adjusting and tooth portion forming for further adjusting flange prototype of slug to be predetermined length and on the periphery of flange forming axial straight row of tooth portion; (5) a step of punching for forming a through hole at the slug and tapping thread on the periphery of the through hole.
 2. The method for extrusion molding of a self-locked nut as claim 1, wherein after punching out the slug to have the through hole, thread is formed on the inner surface of the through hole by a tapping machine.
 3. The method for extrusion molding of a self-locked nut as claim 1, wherein the mold used for the trimming step comprises a nut cavity and a lower cavity communicated with the nut cavity, the nut cavity matching with an upper punch, the lower cavity matching with a lower punch, the shape of nut cavity along horizontal cross section is matched with the shape of self-locked nut along horizontal cross section, and the shape of lower cavity along horizontal cross section is matched with the shape of self-locked nut flange along horizontal cross section.
 4. The method for extrusion molding of a self-locked nut as claim 3, wherein the contact surface between the nut lower cavity and the lower cavity is an arc surface.
 5. The method for extrusion molding of a self-locked nut as claim 3, wherein the prepared slug enters sequentially into three same trimming molds with the slug turned with 180 degrees to enter in to a mold.
 6. The method for extrusion molding of a self-locked nut as claim 1, wherein the mold for the flange pre-forming step of forming flange prototype comprises a nut cavity and a lower cavity, the shape of nut cavity along the horizontal cross section matches with the shape of self-locked nut body along the horizontal cross section, and the contact surface between the nut cavity and the lower cavity is an arc surface but with radius larger than the radius of arc surface of trimming mold, and the nut cavity matching with an upper punch, the lower cavity matching with a lower punch.
 7. The method for extrusion molding of a self-locked nut as claim 6, wherein trimmed slug is rotated by 180 degrees to enter into the mold of the flange pre-forming step.
 8. The method for extrusion molding of a self-locked nut as claim 1, wherein mold of flange adjusting and tooth portion forming step includes nut cavity and lower cavity and an axial straight row tooth portion is formed on the inner wall of lower cavity.
 9. The method for extrusion molding of a self-locked nut as claim 8, wherein slug through flange adjusting and tooth portion forming step is rotated by 180 degrees to perform punching a through hole step. 